This invention relates to an electron beam metrology system for measuring a pattern width on a specimen by scanning with an electron beam, and more particularly to a system of the kind described above which has the function of judging the surface profile of a pattern for acquiring information of surface topography of the pattern.
To meet the recent tendency toward high integration of semiconductor circuits and resultant miniaturization of the width of patterns in circuit elements, there is a growing demand for development of a metrology system which replaces conventional optical metrology systems and measures the pattern width by scanning with an electron beam. Especially, for the purpose of development of a new process, it is necessary to measure and evaluate the width distribution of the same patterns on the entire surface of a specimen in the form of a wafer, and the number of patterns to be measured is very large. Manual measurement is unfit for satisfying the above requirement in view of the length of time required for measurement as well as the limited ability, and a system capable of automatic measurement of many patterns within a short period of time is indispensably required. From the aspect of surface profile, patterns to be measured are broadly classified into a line pattern having a raised profile, a space pattern having a hollow profile, and a line-and-space pattern formed of an alternation of a line pattern and a space pattern.
Figs. 1A and 1B are sectional views of practical examples of a line pattern and a space pattern provided by resist patterns 101 formed on silicon nitride films 100 respectively, and signal waveforms appearing as a result of one-dimensional scanning of these patterns with an electron beam are shown beneath the sectional views respectively. The signal yield of the silicon nitride does not appreciably differ from that of the resist. Consequently, these two signal waveforms are substantially the same in that peaks appear only at the edges of each of the patterns, and mere comparison of these signal waveforms cannot discriminate between the line pattern and the space pattern. Therefore, for the purpose of discrimination, it is necessary to correlate these signal waveforms with the profiles of the measured patterns. In the measurement of the width of a pattern, measurement of the width at the base of the pattern is generally required. As will be seen in the waveforms shown in FIGS. 1A and 1B, the positions of the peaks of the waveform appearing at the edges of the space pattern do not coincide with the corresponding positions of the peaks of the waveform appearing at the edges of the line pattern. Therefore, in order to attain accurate measurement of the pattern width, it is indispensable to process the pattern detection signal in relation to the surface profile of the pattern subjected to the measurement.
Known publications relating to a system of this kind include, for example, JP-A- No. 59-112217.